🔢 Adding and Subtracting Two-Digit Numbers

What you’ll learn

1. Adding and Taking Away TensAdd and subtract round tens mentally, like 45 + 30 = 75 and 82 - 40 = 42.Adding or subtracting whole tens only changes the tens digit — the ones stay still. For 45 + 30, jump up by tens: 55, 65, 75. For 82 - 40, jump back: 72, 62, 52, 42. With ten-jumps you can do two-digit math in your head.
2. Three Small NumbersAdd three one-digit numbers by finding a pair that makes 10 first, like 5 + 7 + 3 = 15.To add three numbers, hunt for two that make 10. In 5 + 7 + 3, the pair is 7 + 3 = 10, then 5 + 10 = 15. This works because numbers can be added in any order and the total never changes.
3. Adding Two Two-Digit NumbersAdd two two-digit numbers by splitting into tens and ones, like 34 + 27 = 61.To add 34 + 27, split both numbers: tens with tens (30 + 20 = 50) and ones with ones (4 + 7 = 11). Combine: 50 + 11 = 61. When the ones make more than 9, ten of them bundle into a new ten — that is regrouping.
4. Subtracting Two Two-Digit NumbersSubtract two two-digit numbers using number-line jumps, like 63 - 28 = 35, and check by adding.For 63 - 28, jump back in pieces: back 20 lands on 43, then back 8 lands on 35. Always check by adding the answer back: 35 + 28 = 63. Choosing the right trick — ten-jumps or splitting — makes you a two-digit champion.

Questions this course answers

Grounded in trusted sources

• Khan Academy Kids
• PBS Kids — early math
• NAEYC — early math learning
• Britannica Kids

Every Wunder lesson is built from real, reputable sources — never invented.

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